Speech communication apparatus equipped with echo canceller

ABSTRACT

A speech communication apparatus of the present invention includes, in addition to an echo canceller for canceling an acoustic echo generated in a hands-free speech space, a chirp signal generating unit and a training unit. The chirp signal generating unit generates a chirp signal adequate for initial training of the echo canceller. The training control unit enables the chirp signal generating unit to generate a chirp signal, when a predetermined condition for starting hands-free speaking is satisfied, and a chirp tone corresponding to the chirp signal to be output as a volume-amplified tone from the hands-free speaker. The echo canceller performs initial training of the echo canceller based on the chirp tone.

FIELD OF THE INVENTION

The present invention relates to a hands-free speech function-equippedapparatus of wire telephones, mobile radio-telephones, portabletelephones, cordless telephones and, in particular, a speechcommunication apparatus equipped with an echo canceller for eliminatingan acoustic echo which is generated from a speaker for hands-free speechinto a microphone, upon reception, in an acoustic environment.

BACKGROUND OF THE INVENTION

Speech communication apparatuses are known which have, in addition to ahandset speaking mode for speaking with a handset, a hands-free speakingmode. In the hands-free speaking mode, speaking is done with a speakerand a microphone for hands-free speech which are provided on thecommunication apparatus body with a handset added thereto, that is,speaking is done with the speaker and microphone in place of thehandset. In the hands-free speaking mode, the user can freely use his orher hands during speaking. In a mobile radio-telephone apparatus, forexample, a driver can speak with both of his or her hands on a steeringwheel. Thus safety is ensured while driving the automobile.

When, however, speaking is done in the hands-free speaking mode, thespeaker's voice is reflected back from the walls and ceiling of theautomobile to generate an acoustic echo around the microphone. Theacoustic echo is largely not desirable on a communication system ofrelatively great transmission loss, in particular, due to severedegeneration of speech quality. With the digital type mobile radiotelephone, for example, a low bit-rate speech encoder is employed forthe effective utilization of a radio frequency. For burst errors, aninterleaving system is used to enhance the burst error correctioncapability. For this reason, the transmission delay for speaking on oneway of two-way communication apparatuses becomes about 100 msec. Whencommunication is conducted in such a state, an echo is undesirablydetected by the user, thus resulting in a large decline in speechquality.

Proposals have been made to employ an echo canceller in this kind ofsystem. The echo canceller estimates the characteristic of an acousticecho path through the use of an adaptive filter and generates a raiseecho having the same characteristic as that on the acoustic echo path.Further, the echo canceller eliminates the false echo from a speechsignal and cancels an acoustic echo component in the speech signal.

However, the echo canceller generally requires lots of time until afalse echo having the same characteristic as that of the acoustic echopath is generated after the acoustic echo path has been estimated.Therefore, no adequate echo cancellation processing is carried out withthe echo canceller immediately after the hands-free speaking is started.An initial echo remains immediately subsequent to the start of thehands-free speaking, thus leading to a decline in speech quality.

SUMMARY OF THE INVENTION

A first object of the present invention is to provide a speechcommunication apparatus which can eliminate the generation of an initialecho immediately after the start of hands-free speaking and providehigh-quality speech.

A second object of the present invention is to provide a speechcommunication apparatus which can briefly and efficiently initiallytrain an echo canceller.

A third object of the present invention is to provide a speechcommunication apparatus which, even if a user performs any particularoperation for initial training of an echo canceller, can positivelyperform the initial training, when necessary, at all times.

A fourth object of the present invention is to provide a speechcommunication apparatus which can naturally perform initial training ofan echo canceller without giving any unnatural feeling to the user andmake an associated circuit simpler and more compact.

A fifth object of the present invention is to provide a speechcommunication apparatus which, even when a speech mode is switched to ahands-free speaking mode during speaking in a handset speech mode, canprevent the generation of an initial echo immediately after the start ofspeaking in the hands-free speaking mode.

In order to achieve the first object of the present invention, a speechcommunication apparatus is provided which includes, in addition to anecho canceller for canceling an acoustic echo generated in a hands-freespeech space, chirp signal generating means for generating a chirpsignal for initial training of the echo canceller and training controlmeans. The training control means outputs, as a volume-amplified tone, achirp tone corresponding to a chirp signal which is generated from thechirp signal generating means in accordance with the creation of apredetermined condition for starting hands-free speaking, and effectsinitial training of the echo canceller based on the chirp tone.

In the arrangement thus set out above, the initial training of the echocanceller is effected before substantial speaking is done at ahands-free speech start time whereby an optimal characteristiccorresponding to the characteristic around a hands-free speech space isset to the echo canceller. Even immediately after the start of thehands-free speaking, an acoustic echo is effectively canceled by theecho canceller so that high-quality speech can be achieved without anyadverse effect from the acoustic echo.

In order to achieve the second object of the present invention, a chirpsignal is used as a training signal. The chirp signal has thecharacteristic of being very small in a ratio of a peak power andaverage power. When, therefore, the initial training of the echocanceller is effected using the chirp signal, it is possible tosignificantly reduce the time necessary for initial training. Even whenthe initial training is effected at the start of the hands-freespeaking, there is less risk that speaking will be disturbed by theinitial training.

In order to achieve the third object of the present invention, thefollowing respective arrangement is employed so that the initialtraining of the echo canceller may be started. That is, the firstarrangement allows detection to be made of the generation of an incomingcall and incoming call response operation and is responsive to thegeneration of the incoming call and incoming call response operation tostart initial training. The second arrangement monitors whether or notthe incoming call is generated and in response thereto starts initialtraining. The third arrangement monitors whether or not a speech link iscreated during a response standby of the communicating party's apparatusafter transmission. In response to the detection of the creation of thespeech link, initial training starts. The fourth arrangement monitors acalling start instruction input operation and in response thereto startsinitial training. The fifth arrangement monitors a dial informationinput operation necessary for a calling originate operation and inresponse thereto starts initial training.

These arrangements ensure that the automatic initial training of theecho canceller occurs when detection is made of an operationindispensable for incoming call and calling signals or a change in stateof the operation. For this reason, no particular operation is necessaryfor the initial training of the echo canceller and the operation can bemade simpler. Further, the initial training is necessarily performedwhen hands-free speaking is done upon calling and incoming calloperations. For this reason, any undesirable shifting of the speech modeto hands-free speaking prior to initial training being effected isprevented.

These effects are effective for the mobile telephones. That is, if thenumber of occupants varies, for example, in an automobile aftertraining, it is necessary to reinitialize operation parameters due to avariation in the acoustic characteristics in the automobile. That is, itis necessary to frequently retrain the echo canceller. According to thepresent invention, the initial training of the canceller isautomatically made, as set out above, at calling and incoming times.This makes any complex operation unnecessary. The inconvenience ofspeaking being started prior to initial training being effected ispositively prevented.

Where initial training has to be done with a keypad, it is necessary andcumbersome to perform a respective training key operation each time theacoustic characteristic of the automobile varies. When such a keyoperation is not done, hands-free speaking starts without the initialtraining being effected, thus resulting in a decline in speech qualityinvolved.

In order to achieve the fourth object of the present invention, a chirptone output for initial training serves also as an operation acknowledgetone at the calling and incoming call operation times or as a tone forinforming the user of its operation state. In the case where initialtraining is started responsive to the incoming call response operation,a chirp tone is output in place of an operation acknowledge tone for theincoming call response operation. In the case where initial training isstarted responsive to the detection of the generation of an incomingcall, a chirp tone is output in place of a ringing tone for informingthe user of the generation of the incoming call signal. Further, in thecase where initial training is started responsive to the inputting of acalling start instruction, a chirp tone is output in place of anoperation acknowledge tone for informing the user of a calling startinstruction input operation. In the case where initial training isstarted responsive to the inputting of dial information, a chirp tone isoutput in place of an operation acknowledge tone for informing the userof the inputting of the dial information.

Since the acknowledge tone for the respective kind of operation and thetone for informing the operation state to the user are shared by thechirp tone, the initial training can be done without the user beingconscious of the presence of the chirp tone. It is, therefore, possibleto obviate the need to provide any circuit for generating an operationacknowledge tone and informing tone. This can make an associate circuitsimpler and more compact.

In order to achieve the fifth object of the present invention, thespeech mode switching operation is monitored during handset speaking.Upon the operation of switching the speech mode from the handsetspeaking mode to the hands-free speaking mode, a chirp tonecorresponding to a chirp signal generated from the chirp signalgenerating means is output as a volume-amplified tone from the speakerand the initial training of the echo canceller is conducted based on thechirp tone.

In the arrangement above, even when the operation of switching thespeech mode from the handset speaking mode to the hands-free speakingmode is carried out during the handset speaking, the initial training ofthe echo canceller is conducted before shifting the speech mode to thehands-free speaking mode. It is thus possible to conduct high qualityhands-free speaking.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit block diagram diagrammatically showing anarrangement of a speech communication apparatus according to a firstembodiment of the present invention;

FIGS. 2A and 2B, each, are a circuit block diagram showing a detailedarrangement of the apparatus of FIG. 1;

FIG. 3 is a circuit block diagram showing an arrangement of an echocanceller provided in the apparatus shown in FIG. 2A;

FIG. 4 is a flow chart for showing an incoming call control procedureand control contents of a control circuit provided in the apparatusshown in FIGS. 2A and 2B;

FIG. 5 is a flow chart showing a calling signal control procedure andcontrol contents of a control circuit shown in FIGS. 2A and 2B;

FIG. 6 is a flow chart for showing an initial training control procedureand control contents of a control circuit shown in FIGS. 2A and 2B;

FIG. 7 is a circuit block diagram showing an arrangement of a speechcommunication apparatus according to a second embodiment of the presentinvention;

FIG. 8 is a circuit block diagram showing an arrangement of an echocanceller provided in the apparatus shown in FIG. 7;

FIG. 9 is a flow chart showing an incoming call control procedure andcontrol contents of a control circuit provided in an apparatus shown inFIG. 7;

FIG. 10 is a flow chart showing a calling signal control procedure andcontrol contents of a control circuit provided in the apparatus shown inFIG. 7;

FIG. 11 is a circuit block diagram showing an arrangement of a speechcommunication apparatus according to a third embodiment of the presentembodiment; and

FIGS. 12A and 12B, each, are a flow chart showing an incoming callcontrol procedure and control contents in a speech communicationapparatus according to a fourth embodiment of the present invention.

DETAILED DESCRIPTION

A first embodiment provides one example of applying the presentinvention to a mobile radio-telephone apparatus having a handsetspeaking function and a hands-free speaking function.

A dual mode system performs radio communication by selectively using ananalog mode and digital mode. In the analog mode, a carrier is, forexample, frequency modulated by an analog speech signal in a transmitcircuit. In a digital mode, a speech signal is encoded and a carrier ismodulated by the encoded speech signal with the use of a digitalmodulation system, such as a π/4 shifted DQPSK (π/4 shifted,differentially encoded quadrature phase shift keying system) andtransmitted.

FIG. 1 is a circuit block diagram showing a schematic arrangement of adual mode mobile radio-telephone apparatus of the present embodiment.

The present apparatus comprises an antenna 1, a radio unit 2, a cradle 3and a handset 4. The antenna 1 is comprised of, for example, an antennamounted on automobile body. The radio unit 2 is arranged, for example,in the trunk of the automobile and connected to the antenna via acoaxial cable. The cradle 3 is disposed, for example, at an armrest inthe automobile and connected to the radio unit 2 via a cable comprisedof a plurality of signal, control and feeder lines twisted together. Thehandset 4 is detachably placed relative to the cradle and connectedrelative to the cradle via a curl cord comprised of signal, control andfeeder lines twisted together,

The radio unit 2 includes a radio circuit section 2a, a speech circuitsection 2b, a radio unit control circuit 2c, a RAM 2d for storing data,etc., necessary for control, a power supply circuit 2e, oscillators 2f,2g and switches 2h, 2i. The speech circuit section 2b includes a digitalspeech circuit used in a digital mode, an analog speech circuit used inan analog mode and an echo canceller 30. To the digital and analogspeech circuits, the oscillators 2f, 2g supply various kinds of clocks.The switches 2h and 2i are turned ON in the digital and analog modes tosupply a power supply voltage for excitation of the oscillators 2f and2g, respectively. The power supply circuit 2e generates a predeterminedoperation power supply voltage Vcc based on the output of an automobilebattery not shown.

The cradle 3 includes a speaker (hereinafter referred to as a hands-freespeaker) 3a for hands-free speaking, a microphone (hereinafter referredto as a hands-free microphone) 3b for hands-free speaking, a cradlecontrol circuit 3c and a hook switch 3d.

The handset 4 comprises a speaker (hereinafter referred to as a handsetspeaker) 4a for handset speaking, a handset control circuit 4c, a keyinput section 4d, and a display unit 4e. The key input section 4d hasdial keys and function keys such as SND and END keys. The SND key isused to input a transmit instruction at an originate time and anacknowledge response at a terminate time. The END key is used to end acall thereby indicating an end of speech. The display unit 4e iscomprised of, for example, a liquid crystal display unit and employed todisplay various items of information, such as the number dialed and thecommunication operation, etc.

FIGS. 2A and 2B show a detailed arrangement of the radio unit 2, cradle3 and handset 4.

First, the operation of the circuit system will be explained below withthe digital mode set. A radio carrier signal from a base station, notshown, via a given radio channel is received at the antenna 1 and theninput to a receiving unit (RX) 22 via a duplexer (DUP) 21. At thereceiving unit 22, a received carrier signal is mixed with a localoscillation signal from a frequency synthesizer 24 to obtain anintermediate frequency signal as a frequency-converted signal. Afterbeing converted by an A/D converter 25 to a digital signal, the receivedintermediate frequency signal is supplied to a digital demodulationcircuit (DEM) 26. At the digital demodulation circuit 26, the receivedintermediate frequency signal is demodulated to obtain a received baseband signal. The received base band signal is subjected by achannel-codec (CH-COD) 27 to error correction and then to speechdemodulation processing by a speech-codec (SP-COD) 28.

The received digital signal output from the speech-codec 28 is input toa change-over switch 29. The change-over switch 29 is controlled suchthat, with the digital mode set, a received speech signal output fromthe speech-codec 28 is selectively output by a control signal $8 outputfrom a radio unit control circuit. With the digital mode in the setstate, therefore, the received speech signal input from the speech-codec28 is input via the change-over switch 29 to an echo canceller (EC-CAN)30. The received digital speech signal passed through the echo canceller30, after being converted to a received analog speech signal, is inputto a change-over switch 32. The change-over switch 32 is controlled suchthat, with the digital mode set, a received analog speech signal outputfrom the D/A converter 31 is selectively delivered as an output with acontrol signal S9 output from the radio unit control circuit 2c. Thereceived analog speech signal is thus passed through the change-overswitch 32.

The received analog speech signal is branched into two routes. Thesignal on one route is supplied via a buffer amplifier 34 and the cradle3 to the handset 4. With the handset speaking mode selected, thereceived speech signal, after being volume-controlled by a volume 4f, isoutput from the handset speaker 4a in the handset 4. With the hands-freespeaking mode selected, the received speech signal, after beingvolume-controlled by a volume 33, is amplified by an amplifier 35 anddelivered to the cradle 3. The received speech signal is output, as avolume-amplified output, from the hands-free speaker 3a on the cradle 3.

A handset transmit speech signal from a user which has been detected bythe handset microphone 4b and then subjected to acoustic/electricconversion is input to a change-over switch 3e on the cradle 3. Thechange-over switch 3e is controlled so that, with the handset speakingmode set, the handset transmit speech signal is selectively output bythe cradle control circuit 3c and with the hands-free speaking mode set,the hands-free transmit speech signal is selectively output. Whether thehandset speaking mode or the hands-free speaking mode is set isdetermined, by the cradle control circuit 3c, in accordance with thestate of the hook switch 3d. The handset speaking mode is determinedwith the handset 4 lifted up from the cradle 3 and the hook switch 3d inan off-hook state. On the other hand, the hands-free speaking mode isdetermined with the handset 4 placed on the cradle 3 and the hook switch3d in an on-hook state. The transmit speech signal output from thechange-over switch 3e is supplied to the radio unit 2 via a switch 3 fand buffer amplifier 3g.

In the radio unit 2, the transmit speech signal, after being convertedto a digital signal by an A/D converter 36, is supplied to the echocanceller 30. In the echo canceller 30, digital signal processingcancels an acoustic echo from the transmit speech signal. The digitaltransmit signal output from the echo canceller 30 is supplied to achange-over switch 37. The change-over switch 37 is controlled suchthat, with the digital mode set, the digital transmit signal is input tothe speech-codec 28 with a control signal S8 output from the radio unitcontrol circuit 2c. In the analog mode set, the digital transmit signalis supplied to a D/A converter 42.

The speech-codec 28 subjects the digital transmit signal to codeprocessing. The coded digital transmit signal is subjected to errorcorrection processing by the channel-codec 27 and then supplied to adigital modulation circuit (MOD) 38. The digital modulation circuit 38modulates the coded digital transmit signal using a modulation signal inaccordance with a radio channel frequency. For example, a π/4 shiftedDQPSK system is employed as a digital modulation system. The modulatedsignal output from the digital modulation circuit 38, after beingconverted to an analog signal, is supplied to a transmit circuit (TX)23. In the transmit circuit 23, the modulated signal is mixed with alocal oscillation signal from the frequency synthesizer 24, converted toa radio frequency band signal and power-amplified to a predeterminedtransmit power level. The radio carrier signal output from the transmitcircuit 23 is fed via the duplexer 21 to the antenna 1 and transmittedfrom the antenna 1 to the base station not shown.

The operation of the circuit system will be explained below with theanalog mode set. A received intermediate frequency signal output fromthe receiving unit 22 is supplied to an analog audio circuit 40. Theanalog audio circuit 40 performs the FM detection of the receivedintermediate frequency signal and analog signal processing, such as thefiltering, low frequency amplification, etc. so that the received analogbaseband speech signal is reproduced.

The received analog speech signal output from the analog audio circuit40 is branched into two routes. Via one of the two branch routes, thereceived analog speech signal is converted by the A/D converter 41 to adigital signal and supplied to the change-over switch 29. Thechange-over switch 29 is controlled such that, with the analog mode set,a received speech signal output from the A/D converter 41 is selectivelydelivered with the control signal S8 output from the radio unit controlcircuit 2c. With the analog mode set, a received speech signal is inputvia the change-over switch 29 to the echo canceller 30 after it has beenoutput from the analog audio circuit 40 and A/D converted by the A/Dconverter 41. After being passed through the echo canceller 30, thereceived digital speech signal is converted by the D/A converter 31 backto an analog signal and supplied to the change-over switch 32. Via theother route, the received analog speech signal is directly input to thechange-over switch 32 without being passed through the echo canceller30.

The change-over switch 32 is controlled such that, with the analog modeset and the handset speaking mode selected, the received analog speechsignal directly coming from the analog audio circuit 40 is selectivelydelivered with the control signal S9 output from the radio unit controlcircuit 2c. With the analog mode set and the hands-free speech modeselected, the received analog speech signal output from the A/Dconverter 31 is selectively delivered as an output.

The received analog speech signal selectively delivered from thechange-over switch 32 is branched into two routes. Via one of theseroutes, the received analog speech signal is fed through the bufferamplifier 34 and cradle 3 to the handset 4. With the handset speakingmode selected, the received analog speech signal, after beingvolume-controlled by the volume 4f in the handset 4, is output from thehandset speaker 4a. With the hands-free speaking mode selected, thereceived speech signal on the other route, after being volume-controlledby a volume 33, is amplified by the amplifier 35 and output from thehands-free speaker 3a in the cradle 3.

The analog transmit speech signal input from the cradle 3 to the radiounit 2 is branched into two routes in the radio unit 2. Via one of theseroutes, the analog transmit speech signal, after being converted to thedigital signal by the A/D converter 36, is input to the echo canceller30 because the hands-free speaking mode is involved. The digitaltransmit speech signal, after the acoustic echo component is canceled bythe echo canceller 30, is supplied via the change-over switch 37 to theD/A converter 42 where the digital transmit speech signal is convertedback to an analog transmit speech signal. The analog transmit speechsignal is input to the change-over switch 43. Via the other route, thebranched analog transmit speech signal is input directly to thechange-over switch 43 without being passed through the echo canceller 30because the handset speaking mode is involved.

The change-over switch 43 is controlled such that, with the hands-freespeaking mode selected, the transmit speech signal passing through theecho canceller 30 is selectively delivered as an output with the controlsignal S9 output from the radio unit control circuit 2c. With thehandset speech mode selected, the transmit speech signal directlysupplied without being passed through the echo canceller 30 isselectively delivered from the change-over switch 43 and supplied to theanalog audio circuit 40. In the analog audio circuit 40, a carriersignal is subjected by the transmit speech signal to FM modulationprocessing. The modulated signal output from the analog audio circuit 40is supplied to the transmit circuit 23. In the transmit circuit, themodulated signal is mixed with a local oscillation signal from thefrequency synthesizer 24, converted to a radio frequency signal andpower-amplified to a predetermined transmit power level. A radio carriersignal output from the transmit circuit 23 is fed via the duplexer 21 tothe antenna 1 and transmitted from the antenna 1 to the base station,not shown.

Oscillators 2g1 and 2g2 generate 60 MHz and 2.048 MHz clocks,respectively. The 60 MHz clock is supplied to the echo canceller 30 andthe 2.048 HMz clock is supplied to the A/D converters 36, 41 and D/Aconverters 31, 42. Oscillators 2f1 and 2f2 generate 80 MHz and 50 MHzclock. The 80 MHz clock is supplied to the speech code demodulationcircuit 28 and the 50 MHz clock is supplied to the digital demodulationcircuit 26 and digital modulation circuit 38. Frequency dividers 44, 45and 46 generate 6.2208 MHz, 1.5 MHz and 194.4 MHz clocks based on theclock (50 MHz) generated from the oscillator 212. The 6.2208 MHz clockis supplied to a D/A converter 39, the 1.5 MHz clock is supplied to theerror correction code demodulation circuit 27, and the 194.4KHz clock issupplied to the A/D converter 25.

FIG. 3 is a circuit block showing an arrangement of the echo canceller30.

The echo canceller 30 comprises an echo canceller body 50 constitutedby, for example, a DSP (digital signal processor) and change-overswitches 51, 52 and 53.

The echo canceller body 50 comprises a received signal memory 50a, anadaptive filter 50b, an arithmetic operation unit 50c, a tap coefficientmemory 50d and a tap coefficient update circuit 50e. The body 50 furthercomprises a chirp signal memory 50f, an inverse convolution computationcircuit 50g, and a write switch 50h for tap coefficient initialization.The receive signal memory 50a stores a digital receive speech signal.The adaptive filter 50b is comprised of a transversal filter. Thisfilter generates a false echo based on the received digital speechsignal stored in the received signal memory 50a and a tap coefficientstored in the tap coefficient memory 50d. The computation circuit 50bperforms digital computation processing for subtracting the false echowhich is generated by the adaptive filter 50b from the received digitalspeech signal. The tap coefficient memory 50d stores the tap coefficientof the adaptive filter 50b therein. The tap coefficient update circuit50e updates the tap coefficient in the tap coefficient memory 50d on thebasis of a residual echo which is output from the arithmetic operationunit 50c.

The chirp signal memory 50f initially stores a training signal seriesf(K) for initial training which is obtained by cutting a chirp signalseries of an M cycle to time points--N+1 to M-1. The character "M" aboveis defined as P≦M, assuming that the order of the adaptive filter 50b isgiven by P. The chirp signal memory 50f reads out the training signalseries f(K), during an initial training period of the echo canceller 30,in accordance with an instruction of the radio unit control circuit 2c.The training signal series f(K) is input to the change-over switch 51.During the initial training period, the change-over switch 51 isswitched by a control signal SS3 which is output from the radio unitcontrol circuit 2c. The training signal series f(K) which is output fromthe chirp signal memory 50f during the initial training period isconvened by the D/A converter 31 to an analog signal via the change-overswitch 51 and then output to the cradle 3. In the cradle 3, the analogsignal is output from the hands-free speaker 3a as a chirp tone (avolume-amplified voice).

The chirp tone is reflected on the window and ceiling of the automobileand picked up, as an acoustic echo, by the hands-free microphone 3b ofthe cradle 3. After being converted by the A/D converter 36 to a digitalsignal, a signal series gj (j=0 to M-1) corresponding to the acousticecho of the chirp tone is input to the change-over switch 52 of theradio unit 2. During the initial training period of the echo canceller30, the change-over switch 52 is switched by a control signal SS2 whichis output from the radio unit control circuit 2c. Thus, the signalseries gj (j=0 to M-1) corresponding to the acoustic echo is suppliedvia the change-over switch 52 to the inverse convolution computationcircuit 50g. In the inverse convolution computation circuit 50g, theinverse convolution computation set out below is carded out using thesignal series gj (j=0 to M-1) corresponding to the acoustic echo. By sodoing, it is possible to estimate an impulse response hi (i=0 to P-1) ofthe acoustic echo. It is to be noted that 02 shows an average electricpower of the chirp signal series. ##EQU1##

The switch 50h for initialization is switched ON in accordance with acontrol signal SS4 which is output from a control circuit 2c after theestimation of an impulse response hi of the acoustic echo by the inverseconvolution computation circuit 50g. The impulse response hi of theacoustic echo estimated by the inverse convolution computation circuit50g is supplied to the tap coefficient memory 50d. The tap coefficientmemory 50d stores, as an initial value of the tap coefficient, theimpulse response hi.

The change-over switches 52 and 53 are controlled so that in thehands-free speaking mode selected, these switches are switched to thecontact b in accordance with the control signals SS2 and SS1 output fromthe radio unit control circuit 2c. These switches are switched to thecontact c in the case where the echo canceller 30 has to be bypassed.

The operation of the mobile radio-telephone apparatus according to thepresent invention will be explained below.

In the standby state, the arrival of an incoming call signal and acalling operation are monitored by the control circuits 2c, 3c and 4c.When, in this state, an incoming call signal arrives from the basestation, not shown, the apparatus starts incoming call control. FIG. 4illustrates a flow chart showing the control procedure and controlcontents of the incoming call control operations.

In the standby state, when the incoming call signal arrives via a pagingchannel, an access channel is established between the base station andthe present apparatus in accordance with a predetermined protocol. Aradio channel (radio speech link) is established based on a speechchannel designation signal sent via the access channel from the basestation (step S4a). When start control information arrives at thepresent apparatus via the radio speech link, the present apparatusdelivers a ringing tone from, for example, a hands-free speaker 3a atstep S4b, thus alarming the user about the arrival of the incoming callsignal. In this state, the user responds to the alarm by lifting up, forexample, the handset 4. Then the apparatus determines the state of anoff-hook operation at step S4c. When the apparatus determines that thehandset is in a handset speaking mode, control shifts to a step S4d toallow speaking in the handset speaking mode. When the apparatus is setto a handset speaking state, control shifts for speech to step S4e. Auser can talk in the handset speaking mode. In the handset speakingmode, the echo canceller 30 is set to be in an inoperative state.

In the handset speaking mode, the apparatus monitors the operation of anEND key and off-hook operation of the handset 4 at steps S4f and S4g,respectively. With the END key depressed, the end of the call isdetermined, thus shifting control to step S4h and returning theapparatus back to a standby state.

If the user depresses a SND key during the alarming of the incoming callsignal, the apparatus determines the hands-free speaking mode to beselected by step S4c and control is shifted for speech. That is, at stepS4i, the echo canceller 30 is set to an operative state and then in step4j control is implemented for allowing hands-free speaking.

With the hands-free speaking in an enabled state, control is shifted tostep S4k, allowing the initial training of the echo canceller 30 to beimplemented. That is, in step S6a, the change-over switches 51, 52 ofthe echo canceller 30 are switched to the contact a and, in this state,a training signal series f(k) of a given length is read out of the chirpsignal memory 50f at step S6b. By so doing, the training signal seriesf(k) is delivered to the received signal route via the change-overswitch 51. After being converted to an analog signal by the D/Aconverter 31 and fed to the hands-free speaker 3a in the cradle 3, thesignal is output as a chirp tone (volume-amplified tone) from thehands-free speaker 3a.

When the chirp tone is output, a corresponding acoustic echo is inputfrom the glass window and ceiling in the automobile to the hands-freemicrophone 3b. A signal corresponding to the acoustic echo is convertedby the A/D converter 36 to a digital signal and then input to the echocanceller 30. A signal series gj corresponding to the acoustic echo isfed via the change-over switch 52 to the inverse convolution computationcircuit 50g in the echo canceller 30. By so doing, the computation ofthe formula (1) above is implemented in the inverse convolutioncomputation circuit 50g on the basis of the signal series gf of theacoustic echo and, it is possible to estimate an impulse response hjacross the hands-free speaking space.

At this time, the control circuit 2c monitors, at step S6c, whether ornot the estimation of the above impulse response is completed. Upon thecompletion of the estimation of the impulse response hi, control isshifted to step S6d and, the control circuit 2c turns the write switch50b ON. At step S6e, the tap coefficient memory 50d is set in thewrite-enabled state. For this reason, an estimate of the impulseresponse hi output from the inverse convolution computation circuit 50gis transferred via the switch 50h to the tap coefficient memory 50d andis stored, as an initial value of the tap coefficient.

The method for high-speed training by chirp signal processing isdescribed in detail in Kamitake "Method for High-Speed Training of EchoCanceller by Chirp Signal Processing" of the "Institute of Electronicsand Communications Engineers of Japan" Technical Bulletin CS82-169 N048.

When the initialization of the tap coefficient is completed, control isshifted from step S6f to step S6g and the control circuit 2c returns thewrite switch 50h to the OFF state. At step S6h, switches the change-overswitches 51 and 52 switch to the contact b. The apparatus starts speechcontrol in step S4e, in a hands-free speaking mode.

Thereafter, the apparatus is placed in the hands-free speaking state andthe user can talk in the hands-free speaking mode. At this time, theecho canceller 30 performs the following operation using, as an initialvalue, the tap coefficient initialized to the tap coefficient memory50d.

The received tone signal demodulated by the speech-codec 28 is input viathe change-over switch 29 to the echo canceller 30. The received tonesignal passes through the echo canceller 30, after being converted to ananalog signal. Thereafter, the received tone signal is subjected, by thevolume 33 and tone amplifier 35, to volume control via the change-overswitch 32 and then output as an amplified volume tone from thehands-free speaker 3a in the cradle 3.

The transmit voice of the user, together with the acoustic echo routedfrom the hands-free speaker 3a, is picked up by the hands-freemicrophone 3b to generate a transmit speech signal. The transmit speechsignal, after being passed through the change-over switch 3e andconverted by the A/D converter 36 to a digital signal in the radio unit2, is input to the echo canceller 30. In the echo canceller 30, anarithmetic operation is performed, in the arithmetic operation unit 50c,for subtracting from the digital transmit speech signal a false echowhich is generated at the adaptive filter 50b. By so doing, it ispossible to cancel the false echo contained in the digital transmitspeech signal. At this time, the generation of a false echo is started,in the adaptive filter 50b, using, as an initial value, the tapcoefficient which is set for initial training. For this reason, the echocanceller 30 performs echo cancellation processing to significantlyreduce a residual echo immediately after the start of the hands-freespeaking.

The digital transmit speech signal whose acoustic echo is canceled issequentially input via the change-over switch 37 to the speech-codec 28and channel-codec 27 for coding processing. The digital transmit speechsignal is transmitted from the transmit circuit 23 via the antenna 1 tothe base station.

After the start of the echo cancellation operation, the echo canceller30 updates the tap coefficient of the adaptive filter 50b approximatelyto an optimum value for the hands-free speech space. To update the tapcoefficient, a normalized learning matching system (NLMS) is employedwhich normalizes, for example, a least-mean-square system. The algorithmof the learning matching system is advantageous for it reduces theamount of computation and provides a better characteristic. The equation(2) below shows an update equation for the learning matching method whena P-degree adaptive filter tap coefficient is represented by hj(,j=1 p):##EQU2## where y(n): a signal input to the arithmetic operation unit50c; and

e(n): a residual echo output from the arithmetic operation unit 50c.

In the hands-free speaking state, the apparatus monitors, at steps S4mand S4n, the END key operation and off-hook operation, respectively. If,in this state, the END key is depressed, control is shifted to step S4hand end-of-call control is carried out, returning the apparatus back toa standby state.

In the hands-free speaking state, when the user lifts up the handset 4from the cradle 3, the apparatus determines that the switching operationis made from the hands-free speaking mode to the handset speaking mode.Then control is shifted from step S4n to step S4o and, here, the echocanceller 30 is turned OFF and then at step S4d the handset speechenabling control is carried out. Then handset speech control is shiftedby step S4e. Thus, the user can continue speaking in the handsetspeaking mode.

Now suppose that, in the handset speaking state, the user places thehandset 4 back to the cradle 3 to switch from the handset speaking modeto the hands-free speaking mode. Then, control is shifted from step S4gto step S4i and the apparatus sets the echo canceller 30 from theinoperative state to the operative state. Then control is shifted tostep S4j to enable hands-free speaking. With the hands-free state in anenabled state, the apparatus implements initial training control at stepS4k. The initial training control procedure and control contents are thesame as those set out in connection with FIG. 6. When the initialtraining of the echo canceller 30 is completed, the apparatus is shiftedto the hands-free speech control at step S41.

That is, even when the speech mode is switched to the hands-freespeaking mode during the handset speaking, the apparatus implements theinitial training of the echo canceller 30 when starting the hands-freespeaking.

The transmit control operation of the mobile radio-telephone apparatusof the present invention will be explained below. FIG. 5 illustrates aflow chart showing the control procedure and control items of theapparatus.

In the standby state, the input operation of a dial number is started bythe user upon transmission to a called party. Then the dial number issequentially input at step S5a and the apparatus stores it in a registerin the handset control circuit 4c. At step S5b, the depression of theSND key is monitored.

In this state, it is assumed that all the digits of the dial number havebeen entered and the SND key has been depressed. Then the apparatusimplements a control operation for establishing a radio channel (accesschannel) to the base station at step S5c. The dialed informationcorresponding to the dial number stored is sent over an access channel.When a speech channel designation signal arrives at the apparatus fromthe base station over the access channel, the apparatus tunes to thedesignated speech channel, thus establishing a speech link at step S5d.

Then control is shifted from step S5d to step S5e and the apparatusdetermines the state of the handset 4. If, for example, the handset isplaced in an off-hook state, the handset speech mode has been selectedstate and control is shifted to step S5f. Here the apparatus makeshandset speech enable control. The apparatus is now placed in thehandset speech enable state and control is shifted to step S5g andhandset speech control is started. Thus, the user can talk in a handsetspeaking mode. While in the handset speaking state, the echo canceller30 is set in an inoperative state.

During the handset speaking, the apparatus monitors, at steps S5h andS5i, the END key depression operation and handset off-hook operation,respectively. When the END key is depressed, control is shifted to stepS4h and end-of-call control is effected, thus returning the apparatus toa standby state.

At a point of time when there is a response at the apparatus of thecalled party, the handset 4 is placed in an on-hook state. When this isdone, the apparatus determines the hands-free speaking mode to be in aselected state, control shifts from step S5e to step S5k and, here, theecho canceller 30 is set to an operative state and then control isshifted to step S5l and hands-free speech enable control is carried out.With the hands-free speaking in an enabled state, the apparatusimplements the initial training of the echo canceller 30 at step S5m.The initial training control procedure and control contents are the sameas set out in connection with FIG. 6. When the initial training of theecho canceller 30 is ended, control is shifted to step S5n and theapparatus provides hands-free speech control and the user can talk inthe hands-free speaking mode.

In the hands-free speaking mode, the apparatus monitors, at step S5o andstep S5p, the END key depression operation and handset off-hookoperation, respectively. When the end key is depressed, control isshifted to step S5j. Here the apparatus implements an end-of-calloperation, thus returning to the standby state.

When, during the hands-free speaking, the handset 4 is placed in theoff-hook state, the operation mode has been switched from the hands-freespeaking mode to the handset speaking mode. At step S5q, the echocanceller 30 is set to the inoperative state and control is shifted tothe S5f and a handset call enable control operation is carded out.

In the handset speaking mode, when the handset 4 is placed in theon-hook state, the operation mode has been switched from the handsetspeaking mode to the hands-free speaking mode. Control is shifted tostep S5k and here the echo canceller 30 is set to an operative state. Atstep S51 hands-free speech enable control is carried out, the initialtraining control of the echo canceller 30 is effected at step S5m. Afterinitial training, control is shifted to step S5n and the apparatusperforms hands-free speech control.

According to the present invention, after the hands-free speech enablecontrol is implemented at an incoming call time in accordance with anincoming call response by the SND key but before the hands-free speakingis substantially started, the initial training of the echo canceller 30is executed with a chirp tone. Further, after the hands-free speechenable control is implemented at a transmit time in accordance with theestablishment of a speech link upon response from the apparatus of thecalled party but before the hands-free speech enable control issubstantially started, the initial training of the echo canceller 30 isdone with a chirp tone. By so doing, an optimal characteristiccorresponding to the hands-free speech space is initialized to the echocanceller 30. Even immediately after the start of the hands-freespeaking, the acoustic echo is effectively canceled by the echocanceller. Therefore, the user can start high-quality hands-freespeaking without being adversely affected by the acoustic echoimmediately after the start of speaking.

According to the present embodiment, since the chirp tone is used as aninitial training signal, it is possible to perform the initial trainingin a very brief period of time. For this reason, in spite of the factthat the initial training is effected at the time of starting hands-freespeaking, the hands-free speaking is smoothly started without impartingany adverse effect, such as noise interference.

According to the present embodiment, where any operation indispensableto the incoming call and calling signals, or a variation in the stateoperation is detected, the initial training of the echo canceller 30 isautomatically carried out. For this reason, it is not necessary toperform any particular operation for the initial training of the echocanceller 30. It is, therefore, possible to perform that operation in asimpler way.

Since the automatic training is effected for each incoming call signalor for each calling signal, the cancellation of the acoustic echo cannormally be done, at the hands-free speech time, based on thecancellation information which is optimal at each time. Even if theacoustic characteristic varies in an occupied space of the automobiledue to a variation in the number of occupants in the automobile duringthe call, it is possible to always conduct a call with the best quality.Further, when there is a break in a power supply during the standbystate and cancellation information is erased in the tap coefficientmemory 50d, then automatic training is effected at the time of startingthe hands-free speaking and, at that time, the optimal cancellationinformation is written into the tap coefficient memory 50d. For thisreason, it is not necessary to protect the storage information in thetap coefficient memory 50d with a back-up power supply. In this way, thecircuit arrangement can be made simpler and more compact. An inexpensivecircuit arrangement can be obtained without the need to providehigh-cost memory elements, such as an EEPROM.

According to the present invention, even where the speech mode isswitched from the handset speaking mode to the hands-free speaking modeeither during a speaking start time or during speaking, the initialtraining of the echo canceller 30 is done before the hands-free speakingis substantially started. The result is initialized to the echocanceller 30. For this reason, speaking is started in the handsetspeaking mode and, even when, during a call, the operator switches tothe hands-free speaking mode, it is possible to shift to the hands-freespeaking mode after the echo canceller 30 effects the initial training.Even if the mode is switched to the speaking mode during a call, it ispossible to start a hands-free speaking of high quality without beingadversely affected by the acoustic echo, even immediately after thestart of speaking.

A second embodiment corresponds to an embodiment in which the presentinvention is applied to a digital, portable telephone equipped with ahandset speaking function and hands-free speaking function.

FIG. 7 illustrates a circuit block showing an arrangement of a digital,portable telephone of the second embodiment. The same reference numeralsare employed in the second embodiment to designate parts or elementscorresponding to those shown in FIGS. 2A and 2B and any further detailedexplanation of them is, therefore, omitted for brevity's sake.

The portable telephone of the present invention comprises an antenna 1and a portable telephone body 5.

A received digital speech signal output from a speech-codec 28 issupplied via an echo canceller 300 to a D/A converter 31 where it isconverted to an analog signal. Then the analog signal is amplified by anamplifier, not shown, and then output as a volume-amplified output froma speaker 5a. The speaker 5a serves not only as a handset speaker, butalso as a hands-free speaker. The amplifier above is comprised of, forexample, a variable gain amplifier. When being used as the handsetspeaker, the speaker has its gain set to deliver a received speechsignal of a small amplitude level. When the speaker is used as ahands-free speaker, its gain is set to deliver a received speech signalof a greater amplitude level.

The telephone body 5 has a microphone 5b which serves as ahandset/hands-free shared microphone. The received speech of the user issensed by the microphone 5b and, after being subjected to anacoustic/electric conversion, is converted by an A/D converter 36 to adigital signal and then input to an echo canceller 300. The echocanceller 300 performs digital signal processing for canceling anacoustic echo component contained in the digital transmit speech signalcoming from the A/D converter 36.

The echo canceller 300 above has an arrangement as will be set outbelow. FIG. 8 illustrates a circuit block showing the arrangement of theecho canceller. In FIG. 8, the same reference numerals are employed todesignate parts or elements corresponding to those shown in FIG. 3 andany further explanation of them is, therefore, omitted.

The echo canceller 300 of the present embodiment has an echo cancellerbody 50 comprised of, for example, a DSP and change-over switches 51 and54.

The echo canceller body 50 comprises a received signal memory 50a, anadaptive filter 50d, an arithmetic operation unit 50e, a tap coefficientmemory 50c, a tap coefficient update circuit 50b, a chirp signal memory50f, an inverse convolution computation circuit 50g and a write switch50h for tap coefficient initialization.

The change-over switches 51 and 54 are controlled in accordance with acontrol signal SS3 coming from a radio unit control circuit 5c. Theswitches 51 and 54 are switched to a contact b for a hands-free speakingmode and to a contact a for an initial training period.

Further, the control circuit (CONT) 5c includes, for example, amicrocomputer as a major control section and a training control means 5dfor performing initial training of the echo canceller 300 in addition tothe normal control function of a means for establishing a speech channelupon transmission and reception, a speech control means, etc.

The training control means 5d implements the control of performing theinitial training of the echo canceller 300 upon transmission andreception when the hands-free speaking mode is selected.

A console unit (CU) 5e includes a key switch group, such as a dial key,SND key and END key and a liquid crystal display unit for displaying anumber dialed, an operation state of the telephone, etc. A power supplycircuit 5f generates a predetermined power supply voltage Vcc based onthe output of, for example, a battery 5g and supplies it to a respectiveassociated circuit.

The operation of the telephone thus arranged will be explained below inaccordance with its control procedure.

In the standby state, the control circuit 5c repeatedly monitors thearrival of incoming call data and the dial key operation upontransmission.

Let it be assumed that the incoming call data arrives from a basestation, not shown. In this state, the control circuit 5c creates aradio speech channel relative to the base station at step S9a as shownin FIG. 9 if the incoming call data is directed to this particularstation. Then, the station is put in an acknowledge enable state. Whenthe radio speech channel has been established, the control circuit 5cdetermines whether the speech mode selected is a handset speaking modeor a hands-free speaking mode. When the handset speaking mode isselected, the control circuit 5c produces a ringing tone as an outputuntil the user responds to the incoming call tone through the operationof the SND key.

When, on the other hand, the hands-free speaking mode is selected as aspeech mode, the control circuit 5c effects the initial training of theecho canceller 300. That is, the control circuit 5c supplies a controlsignal SS3 to the change-over switches 51 and 54 and in the echocanceller 300 at step S9b as shown in FIG. 9, thus switching thechange-over switches 51 and 54 to the contact a. By so doing, a chirpsignal series is read out of the chirp signal memory 50f in a givencycle. The chirp signal series is sequentially output via thechange-over switch 51 to a received signal route. After the chirp signalis converted by the D/A converter 31 to an analog signal, avolume-amplified signal is output as a ringing tone. That is, the chirptone serves also as a ringing tone.

When the chirp tone is an output, an acoustic echo is input to themicrophone 5b due to the chirp tone in the hands-free speechenvironment. A corresponding signal converted by the A/D converter 36 toa digital signal is input to the echo canceller 300. The correspondingsignal series is supplied via the change-over switch 54 to the inverseconvolution computation circuit 50g in the echo canceller 300. In theinverse convolution computation circuit 50g, computation is done basedon the signal series of the acoustic echo and an impulse response isestimated in the hands-free speech environment.

At this time, the control circuit 5c monitors whether or not the impulseresponse has been estimated at step S9d. When the impulse response hasbeen estimated, control is shifted to step S9e and the control circuit5c turns on the write switch 50h. At step S9f, the tap coefficientmemory 50d is set to a write state. For this reason, an estimate of theimpulse response output from the inverse convolution computation circuit50g is transferred via the switch 50h to the tap coefficient memory 50dwhere it is written as an initial value of the tap coefficient.

When the initial setting of the tap coefficient is completed, control isshifted from step S9g to step S9h and the control circuit 5c returns thewrite switch 50h back to the OFF state. The operation of the SND key ismonitored at step S9i. If, in this state, the user is aware of a ringingtone comprised of the chirp tone and responds to it as an acknowledgeresponse through the depression of the SND key, the control circuit 5cswitches the change-over switches 51 and 54 to the contact b at step S9jand stops the chirp tone from being output at step S9k and thereaftercontrol is shifted to step S9l for hands-free speaking.

Thereafter, the telephone is placed in a hands-free speaking operationstate and the user can talk in the hands-free speaking mode. At thistime, the echo canceller 30 performs the following echo cancellationoperation using, as an initial value, the tap coefficient in the tapcoefficient memory 50d.

In the hands-free speaking state, the control circuit 5c monitors theoperation of the END key at step S9m. When the END key is depressed, thecontrol circuit 5c performs end-of-call control, thus returning theapparatus to a standby state.

The transmit control operation of the portable telephone according tothe present invention will be explained below. FIG. 10 is a flow-chartshowing a control procedure and control contents of the telephone.

Let it be assumed that the user dials the number of the called party atthe telephone upon transmission. Each time the dialed number is inputone digit at a time, control is shifted from step S10a to step S10b andthe dial number is stored in a register in the control circuit 5c.

With the dial number entered, the control circuit 5c performs theinitial training of the echo canceller 300. At step S10c, thechange-over switches 51 and 54 are switched to the contact a. At stepS10d, a length of chirp signal series is read out of the chirp signalmemory 50f. Then the chirp signal series is output to the receivedsignal route via the change-over switch 51. After being converted by theD/A converter 31 to an analog signal, the chirp signal is output as adial acknowledge tone, that is, as a volume-amplified tone. That is, thechirp tone for initial training is also used as a dial acknowledge tone.

When the chirp tone is delivered as an output, a corresponding acousticecho from the hands-free speech environment is input to the microphone5b. After being converted by the A/D converter 36 to a digital signal,the chirp signal is sent to the echo canceller 300. A signal seriescorresponding to the acoustic echo is fed via the change-over switch 54to the inverse convolution computation circuit 50g in the echo canceller300. In the inverse convolution computation circuit 50g, computation iscarried out based on the acoustic echo's signal series. By so doing, itis possible to estimate the impulse response in the hands-free speechenvironment.

When the estimation of the impulse response is completed, control isshifted from step S10e to step S10f and the control circuit 5c turns onthe write switch 50h and, at step S10g, sets the tap coefficient memory50d to a write state. For this reason, the estimate of the impulseresponse output from the inverse convolution computation circuit 50g istransferred via the write switch 50h to the tap coefficient memory 50dwhere it is written as an initial value of the tap coefficient to thetap coefficient memory 50d. When the initialization of the tapcoefficient is completed, control is shifted from step S10h to step S10iand the control circuit 5c places the write switch 50h back to the OFFstate. At step S10j, the change-over switches 51 and 54 switch to thecontact b. Thus, the initial training of the echo canceller 300 ends.

Then the control circuit 5c monitors, at steps S10k and step S10, thenext dialed digit and the SND key. When, in this state, the subsequentdigit of the dialed number is entered, control is returned back to stepS10b and the control circuit 4c performs the control of making aninitial training operation at step S10c through step S10j as set out inconnection with the previous embodiment. Thereafter, each time thedigital of the dial number is entered, similarly the control circuit 5cperforms initial training of the echo canceller 300. That is, each timethe digit of the dial number is entered, the initial training of theecho canceller 300 is carried out based on the chirp tone which has beenoutput from the speaker 5b as a dial acknowledge tone.

Let it be assumed all the digits of the dialed number have been inputand the user depresses the SND key. Then the control circuit 5cestablishes a radio channel relative to the base station at step S10m.In establishing the radio channel, dial information is sent out whichcorresponds to the previously entered and stored dial information. Withthe radio channel thus established, the control circuit 5c monitors, atstep S10n, a response from the telephone of the called party on thebasis of that speech link state. When, in this state, the telephone ofthe called party picks up the handset as an off-hook response andestablishes a speech link, control is shifted from step S10n to stepS10o and the control circuit 5c starts the hands-free speech control andthe user can talk in the hands-free speaking mode.

In the hands-free speaking mode, the control circuit 5c monitors theoperation of the END key at step S10p. When, in this state, the END keyis depressed, control is shifted to step S10q and the control circuit 5cestablishes end-of-call control and then returns the telephone to thestandby state.

According to the present invention, since the initial training of theecho canceller 300 is done at the incoming call and calling times, highquality hands-free speech can be achieved without receiving any adverseeffect from the acoustic echo from a time immediately following thestart of speaking. Further, since the initial training is performedduring the incoming call control and calling control preceding thehands-free speaking state, no effect of the initial training is exertedon the hands-free speaking.

According to the present invention, the chirp tone is used as theringing tone and dial acknowledge tone and the user can perform theinitial training smoothly without being made aware of the presence ofthe chirp tone. Further, there is no need to provide an oscillationcircuit for generating a tinging tone and dial acknowledge tone. It isthus possible to simplify the circuit arrangement involved.

In the present invention, the initial training of the echo canceller 300is made based on the chirp tone which is produced as the tinging toneand dial acknowledge tone, thus enabling the initial training to be donein an adequate time. It is thus possible to effect the initial trainingvery accurately.

A third embodiment shows an example in which the present invention isapplied to an analog, portable telephone having a handset speakingfunction and hands-free speaking function.

FIG. 11 illustrates a circuit block showing an arrangement of theanalog, portable telephone. In FIG. 11, the same reference numerals areemployed to designate pans or elements corresponding to those in FIGS.2A, 2B and 7 and any further detailed explanation of them is, therefore,omitted.

The telephone apparatus of the present invention comprises an antenna 1,a portable telephone body 6 and a handset 7 connected via a cuff cord tothe telephone body 6. The handset includes a handset speaker 7a and ahandset microphone 7b.

The telephone body 6 includes not only a circuit system for analogcommunication but also a hands-free speaker 6a, hands-free microphone6b, control circuit (CONT) 6c, and echo canceller 310 comprised of aDSP.

A received intermediate frequency signal output from a receiving circuit3 is frequency modulated by an analog speech demodulation circuit(AUDDEM) 61 to a baseband received speech signal and then converted byan A/D converter 62 to a digital signal for input to the echo canceller310. The digital received speech signal is supplied to the echocanceller 310 on one branched route and input to a D/A converter 63 onthe other route via a change-over switch 51 so that the digital signalis converted to an analog signal. The analog signal is supplied via achange-over switch 64 to a hands-free speaker 6a where it is output as avolume-amplified tone.

A speaking tone of the user and an acoustic echo operation produced fromaround the hands-free speaker 6a are picked up by the hands-freemicrophone 6b and, being subjected to an acoustic/electric conversion,input via a change-over switch 65 to an A/D converter 66. After acorresponding signal is converted by the A/D converter 66 to a digitalsignal for input to the echo canceller 310, the digital signal is inputvia a change-over switch 52 to an arithmetic operation unit 50c in theecho canceller 310. The arithmetic operation unit 50c subtracts, fromthe digital transmit speech signal, a false echo produced from anadaptive filter 50b and cancels an acoustic echo component contained inthe digital transmit speech signal. A digital transmit speech signalproduced from the arithmetic operation unit 50c in the echo canceller310 is converted by a D/A converter 67 to an analog transmit signal viaa change-over switch 53. The analog transmit signal is input to ananalog speech modulation circuit (AUDMOD) 68 where a correspondingtransmit carrier signal is, for example, frequency modulated by theanalog transmit speech signal. The modulated transmit carrier signal isfrequency converted by a transmit circuit 23 to a radio channelfrequency, amplified to a predetermined transmit power level, andtransmitted via a duplexer 21 to a base station, not shown.

The change-over switches 51, 52, and 53 are located outside a DSPcircuit of the echo canceller 310. The echo canceller 310 comprises areceived signal memory 50a, an adaptive filter 50b, an arithmeticoperation unit 50c, a tap coefficient memory 50d, a tap coefficientupdate circuit 50e, a chirp signal memory 50f, an inverse convolutioncomputation circuit 50g and a write switch 50h for tap coefficientinitialization.

In FIG. 11, a console unit (CU) 6d includes a key switch group, such asdial keys, a SND key, END key and speech mode designation key and aliquid crystal display unit for displaying a called party's dialednumber, the operation state of the apparatus, etc. A power supplycircuit 6e generates a predetermined power voltage Vcc based on, forexample, the output of a battery 6f and supplies it to each associatedcircuit.

In the arrangement above, when the handset speaking mode is designated,the change-over switches 64 and 65 are switched to the handset 7 side bya change-over control signal SS1 which is output from the controlcircuit 6c. For this reason, the handset speaker 7a in the handset 7 isconnected to the D/A converter 63 in a receive circuit system and thehandset microphone 7b in the handset 7 is connected to the A/D converter66 in a transmit circuit system. Further, the change-over switches 53and 52 are switched to a short-circuiting side in accordance with thechange-over control signals SS1 and SS2. In the transmit circuit system,therefore, a direct connection is achieved between the A/D converter 66and the D/A converter 67.

When speech is made in this mode, a received speech signal reproduced inthe receive circuit system is output from the handset speaker 7a in thehandset 7. In the transmit circuit system, the user's speech signaldetected by the handset microphone 7b in the handset 7 and subjected toan acoustic/electric conversion is input to the analog speech conversioncircuit 68. A radio carrier signal which is frequently modulated by thetransmit speech signal is transmitted toward the base station. In thisway, handset speaking is carried out.

Now let it be assumed that the user operates the mode designation switchof the console unit 6d selecting the hands-free speaking mode. At a timewhen an incoming call response operation at an incoming call time or aSND key operation at a calling time is performed, the control circuit 6cinitially trains the echo canceller 310. That is, the control circuit 6coutputs the change-over control signal SS1 to the change-over switches64, 65 and 53 and the change-over switches 64 and 65 are switched to thehands-free speaker 6a side and hands-free microphone 6b side,respectively, and the change-over switch 53 is switched to thearithmetic operation unit 50c side in the echo canceller 310. Thecontrol circuit delivers the change-over control signal SS3 to thechange-over switch 51 to switch the change-over switch 51 to the chirpsignal memory 50f. The control circuit delivers the change-over controlsignal SS2 to the change-over switch 52 to switch the change-over switch52 to an inverse convolution computation circuit 50g side in the echocanceller 310. In this state, a chirp signal series is read out of thechirp signal memory 50f.

By so doing, a given length of a chirp signal series is read out of thechirp signal memory 50f, converted by the D/A converter 63 to an analogsignal, and supplied via the change-over switch 64 to the hands-freespeaker 6a where a chirp tone is output as a volume-amplified tone. Anacoustic echo resulting from the chirp tone produced from around thehands-free microphone 6b is converted by the A/D converter 66, and inputto the inverse convolution computation circuit 50g in the echo canceller310 via the change-over switch 52. The inverse convolution computationcircuit 50g performs an inverse convolution computation based on thedigital signal series corresponding to the acoustic echo, thusestimating an impulse response of the acoustic echo. Upon the completionof that estimation, the control circuit 5c turns the write switch 50hON. An estimate of the impulse response obtained from the inverseconvolution computation circuit 50g is transferred via the write switch50h to the tap coefficient memory 50d where an initial value of the tapcoefficient is written.

At the completion of the initial training of the echo canceller 310, thechange-over switch 50h is turned OFF and the control circuit 5c switchesthe change-over switch 51 from the echo canceller 310 side to thereceive route side and the change-over switch 52 from the inverseconvolution computation side to the arithmetic operation unit 50c side.Thereafter, the echo canceller 310 is placed in a learning mode and theapparatus is placed in the hands-free speaking state.

According to the present embodiment, an analog, portable telephoneapparatus can cancel an acoustic echo produced at a hands-free speakingmode and can perform high quality hands-free speaking.

A fourth embodiment is directed to a mobile radio telephone apparatushaving a handset speaking mode and hands-free speaking mode, in which,even if the handset speaking mode is selected at an incoming call timeand at a calling time, the initial training of the echo canceller can bedone as if the hands-free speaking mode is selected.

FIGS. 12A and 12B, each, are a flow chart showing a control procedureand control contents of the present apparatus. When, in these Figures,an incoming call signal is detected, the apparatus implements thecontrol of establishing a radio channel relative to a base station atstep S12a. With the radio channel thus established, a ringing tone isoutput from the hands-free speaker, for example, at step S12b, thusinforming the user of an arrival of an incoming call signal. In thisstate, let it be assumed that the user responds by, for example, liftingup the handset. Then the apparatus detects an incoming call responseoperation at step S12c and enables a shift to the initial training ofthe echo canceller.

That is, the apparatus first sets the echo canceller in an operativestate at step S12d and implements hands-free speech enable control atstep S12e. With hands-free speaking, enabled control is shifted to stepS12f for performing the initial training of the echo canceller using achirp tone. The control procedure and control contents of the initialtraining is shown in FIG. 6.

At the completion of the initial training of the echo canceller, controlis shifted to step S12g and the apparatus determines whether theprevious incoming call response operation is done through the operationof the SND key or by lifting the handset.

If the incoming call response operation is done through the operation ofthe SND key, the apparatus determines that the hands-free speaking modeis selected. Control is shifted to step S12p and the apparatus startshands-free speech control. Hereinafter, the user can talk in thehands-free speaking mode. At this time, the echo canceller startscanceling an acoustic echo contained in a transmit speech signal usingthe initialized tap coefficient as an initial value.

In the hands-free speaking state, the apparatus monitors the operationof the END key and off-hook operation of the handset at step S12q andS12r, respectively. When, in this state, the END key is depressed,control is shifted to step S12 and the apparatus carries out end-of-callcontrol, thus being returned to the standby state.

When, on the other hand, the incoming call response operation is made bylifting the handset, the apparatus determines that the handset speakingmode has been selected. The apparatus makes handset speaking mode enablecontrol. That is, the echo canceller is set to an inoperative state atstep S12h and then performs handset speech control at step S12i. Whenthe apparatus sets the receiving circuit system and transmit circuitsystem in the handset speaking state, the apparatus starts handsetspeech control at step S12j. Thus the user can talk in the handsetspeaking mode.

In the handset speaking state, the apparatus monitors the END keyoperation and handset on-hook operation at steps S12k and S12. With theEND key depressed, the apparatus performs end-of-call control at stepS12o and is returned to a standby state.

Let it be assumed that, in order to switch the speech mode from thehandset speaking mode to the hands-free speaking mode, the handset isreturned back to the cradle. Control is shifted from step S12l to stepS12m and the apparatus first sets the echo canceller from an inoperativestate to an operative state. Control is shifted to step S12n and theapparatus performs hands-free speech control. With the apparatus set inthe hands-free speech state, step S12p shifts control to the hands-freespeech control.

That is, let it be assumed that during handset speaking, the speech modeis switched to the hands-free speaking mode. At this time, the initialtraining of the echo canceller is omitted and a shift is made to thehands-free speaking mode.

Although incoming call control has been done, it is possible even at thetransmit control to implement initial training, at a point in time whenit is detected that the speech link is established. A similar operationcan be carried out by shifting the speech mode to a corresponding speechstate involved after the initial training has been completed.

In the present embodiment, at the creation of the speech link uponincoming call response operation and at a calling time, the initialtraining of the echo canceller is carried out either at the hands-freespeaking mode or at the handset speaking mode and speech control is madein accordance with a speech mode selected after completion of theinitial training. In the case where the operation of switching thespeech mode to the hands-free speaking mode is carried out duringhandset speaking, the speech state can immediately be shifted to ahands-free free speaking state at that time without the initial trainingof the echo canceller. It is, therefore, possible to very briefly andsmoothly switch modes during speaking thereby enhancing the speechquality.

The present invention is not restricted to the preceding embodimentsabove. Although, in the second embodiment, the initial training of theecho canceller has been explained as being done, at the incoming calltime, by outputting a chirp tone in place of a ringing tone, the initialtraining may be effected by outputting the chirp tone in place of theoperation acknowledge tone of the SND key. Instead of performing initialtraining by outputting a chirp tone in place of the dial acknowledgetone, it is also possible to carry out the initial training byoutputting a chirp tone in place of the ringing tone.

In the third embodiment, with the handset speaking state set, the A/Dconverter 62 and D/A converter 63 are provided on the transmit route andthe A/D converter 66 and D/A converter 67 are provided on the receiveroute. Bypass circuits each including a switch are provided such thatone of the associated switches is connected in parallel with the A/Dconverter 62 and D/A converter 63 and the other associated switch isconnected in parallel with the A/D converter 66 and D/A converter 67.Those transmit and receive routes may be provided, without passingthrough the A/D converters 62 and 66 and D/A converters 63 and 67, inwhich case these switches of the bypass circuits are turned ON duringthe handset speech period. By so doing, it is possible to eliminateprocessing delay and signal distortion at the A/D converters 62, 66 andD/A converters 63, 67 and, therefore, to realize high quality handsetspeaking. It is also possible to decrease wasteful power consumption byinterrupting a power supply to the A/D converters 62, 66, and D/Aconverters 63, 67. This advantage is very useful in those apparatuses,such as the portable telephone apparatuses and cordless telephoneapparatuses in particular, using a battery as a power supply, becausethe battery life can be extended.

As shown in Japanese Patent Application H3-339296, corresponding to U.S.patent application Serial No. 07/800,426, etc., having its subjectmatter incorporated into the present invention by reference, in order torender the echo canceller in an operative/inoperative state, a powersupply to the echo canceller may be turned ON/OFF or a supply of anoperation clock signal may also be made or interrupted.

Further, the circuit arrangement of the echo canceller, the controlprocedure and control contents of the initial training control means,the various arrangements of those apparatuses to which the presentinvention are applied can be variously changed or modified withoutdeparting from the spirits and scope of the present invention.

We claim:
 1. A communication apparatus comprising:a receiver forreceiving a first speech signal; a chirp signal generator for generatinga chirp signal; a speaker for selectively outputting the first speechsignal and the chirp signal; a microphone for generating a transmitsignal in accordance with a second speech signal; and an echo cancelercircuit including estimating means for estimating an acoustic echoassociated with an acoustic echo path from said speaker to saidmicrophone based on an acoustic echo of either the first speech signalor the chirp signal, and subtracting the estimated acoustic echo fromthe transmit signal.
 2. The communication apparatus according to claim1, further comprising:detecting means for detecting a predeterminedstate for starting hands-free operation of said communication apparatus;a control circuit including first control means for controlling saidspeaker to output the chirp signal if the predetermined state isdetected and second control means for controlling said echo cancelercircuit to estimate the acoustic echo based on the acoustic echo of thechirp signal.
 3. A communication apparatus comprising:a receiver forreceiving a first speech signal; tone generating means for generating anincoming call acknowledge tone when a call is incoming; a chirp signalgenerator for generating a chirp signal; a handset speaker foroutputting the first speech signal; a hands-free speaker for selectivelyoutputting the first speech signal, the chirp signal, and the incomingcall acknowledge tone; a microphone for generating a transmit signal inaccordance with a second speech signal; an echo canceler circuitincluding estimating means for estimating an acoustic echo associatedwith an acoustic echo path from said speaker to said microphone based onan acoustic echo of either the first speech signal or the chirp signal,and subtracting the estimated acoustic echo from the transmit signal;selecting means, responsive to a user signal following generation of theincoming call acknowledge tone, for selecting one of a hands-freespeaking state in which said hands-free speaker selectively outputs thefirst speech signal and the chirp signal and a handset speaking state inwhich said handset speaker outputs the first speech signal; detectingmeans, responsive to said selecting means, for detecting the hands-freespeaking state; and a control circuit including first control means forcontrolling said hands-free speaker to output the chirp signal if thehands-free speaking state is detected and second control means forcontrolling said echo canceler circuit to estimate the acoustic echobased on the acoustic echo of the chirp signal.
 4. The communicationapparatus of claim 3, wherein said first control means effects output ofthe chirp signal from said hands-free speaker as the incoming callacknowledge tone when said detecting means detects the hands-freespeaking state.
 5. The communication apparatus of claim 3, wherein saidfirst control means effects output of the incoming call acknowledge tonefollowed by the chirp signal from said hands-free speaker when saiddetecting means detects the hands-free speaking state.
 6. Acommunication apparatus comprising:a receiver for receiving a firstspeech signal; a chirp signal generator for generating a chirp signal; aspeaker for selectively outputting either the first speech signal or thechirp signal; a microphone for generating a transmit signal inaccordance with a second speech signal; an echo canceler circuitincluding estimating means for estimating an acoustic echo associatedwith an acoustic echo path from said speaker to said microphone based onan acoustic echo of either the first speech signal or the chirp signal,and subtracting the estimated acoustic echo from the transmit signal;incoming call detecting means for detecting an incoming call signal; anda control circuit including first control means for controlling saidspeaker to output the chirp signal if said detecting means detects theincoming call signal and second control means for controlling said echocanceler circuit to estimate the acoustic echo based on the acousticecho of the chirp signal.
 7. The communication apparatus of claim 6wherein said first control means effects output of the chirp signal asan alarm tone from said speaker when said detecting means detects theincoming call signal.
 8. The communication apparatus of claim 6 furthercomprising alarm tone generating means for generating an alarm toneresponsive to the said detecting means detecting the incoming callsignal, said speaker outputting said alarm tone, wherein said firstcontrol means effects output of the chirp signal from said speaker atleast one of prior to output of an alarm tone, between output of twoalarm tones, and following output of the alarm tone.
 9. A communicationapparatus comprising:a receiver for receiving a first speech signal; achirp signal generator for generating a chirp signal; a speaker forselectively outputting either the first speech signal or the chirpsignal; a microphone for generating a transmit signal in accordance witha second speech signal; an echo canceler circuit including estimatingmeans for estimating an acoustic echo associated with an acoustic echopath from said speaker to said microphone based on an acoustic echo ofeither the first speech signal or the chirp signal, and subtracting theestimated acoustic echo from the transmit signal; detecting means fordetecting creation of a speech link between said communication apparatusand another communication apparatus; and a control circuit includingfirst control means for controlling said speaker to output the chirpsignal if said detecting means detects the creation of the speech linkand second control means for controlling said echo canceler circuit toestimate the acoustic echo based on the acoustic echo of the chirpsignal.
 10. A communication apparatus comprising:a receiver forreceiving a first speech signal; a chirp signal generator for generatinga chirp signal; a speaker for selectively outputting either the firstspeech signal or the chirp signal; a microphone for generating atransmit signal in accordance with a second speech signal; an echocanceler circuit including estimating means for estimating an acousticecho associated with an acoustic echo path from said speaker to saidmicrophone based on an acoustic echo of either the first speech signalor the chirp signal, and subtracting the estimated acoustic echo fromthe transmit signal; input means for inputting a call start instructionto initiate a calling operation; and a control circuit including firstcontrol means for controlling said speaker to output the chirp signal ifsaid input means inputs the call start instruction and second controlmeans for controlling said echo canceler circuit to estimate theacoustic echo based on the acoustic echo of the chirp signal.
 11. Thecommunication apparatus of claim 10 wherein said first control meanseffects output of the chirp signal as an outgoing call acknowledge tonewhen the call start instruction is input by said input means.
 12. Thecommunication apparatus of claim 10 further comprising means forgenerating an outgoing call acknowledge tone, said speaker outputtingthe outgoing call acknowledge tone, wherein said first control meanseffects output from said speaker of the outgoing call acknowledge tonefollowed by the chirp signal when the call start instruction is input bysaid input means.
 13. A communication apparatus comprising:a receiverfor receiving a first speech signal; a chirp signal generator forgenerating a chirp signal; a speaker for selectively outputting eitherthe first speech signal or the chirp signal; a microphone for generatinga transmit signal in accordance with a second speech signal; an echocanceler circuit including estimating means for estimating an acousticecho associated with an acoustic echo path from said speaker to saidmicrophone based on an acoustic echo of either the first speech signalor the chirp signal, and subtracting the estimated acoustic echo fromthe transmit signal; input means for inputting dial information for acalling operation; and a control circuit including first control meansfor controlling said speaker to output the chirp signal if said inputmeans inputs the dial information and second control means forcontrolling said echo canceler circuit to estimate the acoustic echobased on the acoustic echo of the chirp signal.
 14. The communicationapparatus of claim 13 wherein said first control means effects output ofthe chirp signal from said speaker as an outgoing call acknowledge tonewhen the dial information is input by said input means.
 15. Thecommunication apparatus of claim 13 further comprising means forgenerating an outgoing call acknowledge tone, said speaker outputtingthe outgoing call acknowledge tone, wherein said first control meanseffects output from said speaker of the outgoing call acknowledge tonefollowed by the chirp signal when the dial information is input by saidinput means.
 16. A speech communication apparatus comprising:a firstspeaker for handset speaking and for outputting a first received signal;a first microphone for handset speaking and for generating a firsttransmit signal; a chirp signal generator for generating a chirp signal;a second speaker for hands-free speaking and for selectively outputtingeither a second received signal or the chirp signal; a second microphonefor hands-free speaking for generating a second transmit signal;selecting means for selecting one of a handset speaking mode and ahands-free speaking mode; a first controller, responsive to selection ofthe handset speaking mode by said selecting means, for connecting saidfirst speaker to a first received signal path and said first microphoneto a first transmit signal path; a second controller, responsive toselection of the hands-free speaking mode by said selecting means, forconnecting said second speaker to a second received signal path and saidsecond microphone to a second transmit signal path; an echo cancelerincluding estimating means for estimating an acoustic echo associatedwith an acoustic echo path from said second speaker to said secondmicrophone, and subtracting the estimated acoustic echo from the secondtransmit signal; a control circuit, responsive to selection of thehands-free speaking mode by said selecting means when in the handsetspeaking mode, including first control means for controlling said secondspeaker to output the chirp signal when said second controller connectssaid second speaker to the received signal path and said secondmicrophone to the transmit signal path and second control means forcontrolling said echo canceler to estimate the acoustic echo based onthe acoustic echo of the chirp signal.
 17. The speech communicationapparatus of claim 16 further comprising:a handset, said handsetincluding said first speaker and said first microphone; and a cradle,said cradle including said second speaker and said second microphone,wherein responsive to placement of said handset on said cradle duringsaid handset speaking mode, said first control means effects output ofthe chirp signal from said second speaker.
 18. The speech communicationapparatus of claim 16 wherein responsive to selection of the hands-freespeaking mode by said selecting means when in the handset speaking mode,said second control means effects operation of said echo canceler andsaid first control means effects output of the chirp signal from saidsecond speaker.
 19. A speech communication apparatus comprising:a firstspeaker for handset speaking; a first microphone for handset speaking; achirp signal generator for generating a chirp signal; a second speakerfor hands-free speaking and outputting the chirp signal; a secondmicrophone for hands-free speaking and for generating a transmit signal;an echo canceler circuit including estimating means for estimating anacoustic echo associated with an acoustic echo path from said secondspeaker to said second microphone based on an acoustic echo of the chirpsignal, and subtracting the estimated acoustic echo from the transmitsignal; generating means for generating an incoming call signal and forgenerating an outgoing calling signal; detecting means for detecting thegeneration of the incoming call signal and the outgoing calling signal;speaking mode selecting means for selecting one of a handset speakingmode and a hands-free speaking mode; a control circuit, responsive todetection of at least one of the incoming call signal and the outgoingcalling signal by the detecting means, including first control means forcontrolling said second speaker to output the chirp signal prior toentering either the handset speaking mode or the hands-free speakingmode and second control means for controlling said echo canceler circuitto estimate the acoustic echo based on the acoustic echo of the chirpsignal; a speech controller, responsive to said speaking mode selectingmeans, for entering one of the handset speaking mode and the hands-freespeaking mode following said echo canceler circuit estimating anacoustic echo based on the acoustic echo of the chirp signal.